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The timeline of life on earth

 


In a recent study published in Proceedings of the National Academy of Sciences, (PNAS), scientists at the Carnegie Science Institute claim that chemical signs of photosynthesis, and so of life, have shown up in rocks at least 2.5 billion years old. Vegetative life existed on earth that far back. Until now, photosynthesis was generally traced back only to 1.7 billion. 

"Good for the scientists," you might say, "it clearly helps make them stand-outs within their special field of study.  But should it matter to the rest of us?"

I submit that it should.  One reason is that as one pushes back the dating of the earliest emergence of life, one shortens the amount of time for the chemical, pre-biological evolution that may have been necessary to get the history of life underway.

How long a span of time is necessary for life to emerge on a planet, when circumstances (such as the distance to the nearest sun, the size of that sun, etc.) are amenable? There is only one case -- that of our own planet -- for which we can really study the matter as yet.  But in principle the question should be subject to a general answer based on natural laws, perhaps some of which will prove to be as yet unknown to us.

When did the earth first form, AS a solid planet? Best guesses at present are in the neighborhood of 4.5 billion years ago. If photosynthesis is 2.5 billion years ago, then simpler forms of life are presumably older.  We may be able to push them back to, say, 3.3 billion years ago,  PNAS suggests. This means there can be no natural laws that prohibit the development of life within 1.2 billion years of the formation of a suitable planet.  

That is good to know.    


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